Coccinelle is a tool for pattern matching and text transformation that has
many uses in kernel development, including the application of complex,
tree-wide patches and detection of problematic programming patterns.

The semantic patches included in the kernel use features and options
which are provided by Coccinelle version 1.0.0-rc11 and above.
Using earlier versions will fail as the option names used by
the Coccinelle files and coccicheck have been updated.

Coccinelle is available through the package manager
of many distributions, e.g. :

Debian

Fedora

Ubuntu

OpenSUSE

Arch Linux

NetBSD

FreeBSD

Some distribution packages are obsolete and it is recommended
to use the latest version released from the Coccinelle homepage at
http://coccinelle.lip6.fr/

By default, coccicheck tries to run as parallel as possible. To change
the parallelism, set the J= variable. For example, to run across 4 CPUs:

make coccicheck MODE=report J=4

As of Coccinelle 1.0.2 Coccinelle uses Ocaml parmap for parallelization,
if support for this is detected you will benefit from parmap parallelization.

When parmap is enabled coccicheck will enable dynamic load balancing by using
--chunksize1 argument, this ensures we keep feeding threads with work
one by one, so that we avoid the situation where most work gets done by only
a few threads. With dynamic load balancing, if a thread finishes early we keep
feeding it more work.

When parmap is enabled, if an error occurs in Coccinelle, this error
value is propagated back, the return value of the makecoccicheck
captures this return value.

Using coccicheck is best as it provides in the spatch command line
include options matching the options used when we compile the kernel.
You can learn what these options are by using V=1, you could then
manually run Coccinelle with debug options added.

Alternatively you can debug running Coccinelle against SmPL patches
by asking for stderr to be redirected to stderr, by default stderr
is redirected to /dev/null, if you’d like to capture stderr you
can specify the DEBUG_FILE="file.txt" option to coccicheck. For
instance:

KBUILD_EXTMOD is set when an explicit target with M= is used. For both cases
the spatch –dir argument is used, as such third rule applies when whether M=
is used or not, and when M= is used the target directory can have its own
.cocciconfig file. When M= is not passed as an argument to coccicheck the
target directory is the same as the directory from where spatch was called.

If not using the kernel’s coccicheck target, keep the above precedence
order logic of .cocciconfig reading. If using the kernel’s coccicheck target,
override any of the kernel’s .coccicheck’s settings using SPFLAGS.

We help Coccinelle when used against Linux with a set of sensible defaults
options for Linux with our own Linux .cocciconfig. This hints to coccinelle
git can be used for gitgrep queries over coccigrep. A timeout of 200
seconds should suffice for now.

The options picked up by coccinelle when reading a .cocciconfig do not appear
as arguments to spatch processes running on your system, to confirm what
options will be used by Coccinelle run:

spatch --print-options-only

You can override with your own preferred index option by using SPFLAGS. Take
note that when there are conflicting options Coccinelle takes precedence for
the last options passed. Using .cocciconfig is possible to use idutils, however
given the order of precedence followed by Coccinelle, since the kernel now
carries its own .cocciconfig, you will need to use SPFLAGS to use idutils if
desired. See below section “Additional flags” for more details on how to use
idutils.

Additional flags can be passed to spatch through the SPFLAGS
variable. This works as Coccinelle respects the last flags
given to it when options are in conflict.

make SPFLAGS=--use-glimpse coccicheck

Coccinelle supports idutils as well but requires coccinelle >= 1.0.6.
When no ID file is specified coccinelle assumes your ID database file
is in the file .id-utils.index on the top level of the kernel, coccinelle
carries a script scripts/idutils_index.sh which creates the database with:

mkid -i C --output .id-utils.index

If you have another database filename you can also just symlink with this
name.

make SPFLAGS=--use-idutils coccicheck

Alternatively you can specify the database filename explicitly, for
instance:

make SPFLAGS="--use-idutils /full-path/to/ID" coccicheck

See spatch--help to learn more about spatch options.

Note that the --use-glimpse and --use-idutils options
require external tools for indexing the code. None of them is
thus active by default. However, by indexing the code with
one of these tools, and according to the cocci file used,
spatch could proceed the entire code base more quickly.

As Coccinelle features get added some more advanced SmPL patches
may require newer versions of Coccinelle. If an SmPL patch requires
at least a version of Coccinelle, this can be specified as follows,
as an example if requiring at least Coccinelle >= 1.0.5:

This SmPL excerpt generates entries on the standard output, as
illustrated below:

/home/user/linux/crypto/ctr.c:188:9-16: ERR_CAST can be used with alg
/home/user/linux/crypto/authenc.c:619:9-16: ERR_CAST can be used with auth
/home/user/linux/crypto/xts.c:227:9-16: ERR_CAST can be used with alg

context highlights lines of interest and their context
in a diff-like style.

NOTE: The diff-like output generated is NOT an applicable patch. The
intent of the context mode is to highlight the important lines
(annotated with minus, -) and gives some surrounding context
lines around. This output can be used with the diff mode of
Emacs to review the code.

This SmPL excerpt generates Org entries on the standard output, as
illustrated below:

* TODO [[view:/home/user/linux/crypto/ctr.c::face=ovl-face1::linb=188::colb=9::cole=16][ERR_CAST can be used with alg]]
* TODO [[view:/home/user/linux/crypto/authenc.c::face=ovl-face1::linb=619::colb=9::cole=16][ERR_CAST can be used with auth]]
* TODO [[view:/home/user/linux/crypto/xts.c::face=ovl-face1::linb=227::colb=9::cole=16][ERR_CAST can be used with alg]]